A non-invasive screening study of varnishes applied to three paintings by Edvard Munch using portable diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)

Abstract

The availability and popularity of portable non-invasive instrumentation for the study of paintings has increased due to a shift away from using micro-invasive techniques. Fourier transform infrared spectroscopy (FTIR) is a successful and established technique for the characterisation of organic materials in varnish coatings and paint films. In addition, portable FTIR (pFTIR) spectrometers allow for non-invasive in situ analyses. This overcomes the disadvantages associated with micro-sampling and reproducibility issues encountered in analysis at a specific spot, as pFTIR enables examination of the whole painting. However, the practical applications and capabilities of pFTIR as a suitable screening method for the chemical characterization of varnish coatings in painting collections require systematic evaluation. This study involves a selection of three paintings from the collection of 57 works by Edvard Munch belonging to The National Museum of Art in Norway. Its focus is the identification of the non-original varnish types that were applied by the museum. Between 1909 and 1993, the Museum was embroiled in a varnish controversy due to their application of, first natural and then synthetic, varnish coatings to 48 of these Munch paintings. A series of public debates arose about the Museum's varnishing practice, which ran counter to the artist's usual custom of leaving paint surfaces unvarnished (or occasional locally varnished). The three paintings were screened using a pFTIR spectrometer. Different regions of the varnished and unvarnished painted surfaces were analysed with Portable Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). These paintings date from 1887 to 1891 and are documented as having been treated at the Museum with one of the following types of natural or low-molecular-weight synthetic varnish coatings: dammar, mastic, polycyclohexanone (Laropal K 80 from BASF) and reduced or hydrogenated cyclohexanone-co-methyl-cyclohexanone (MS2A from Howards of Ilford). Surface microscopy and multispectral imaging of the varnished surfaces initially assisted the mapping and choice of areas relevant for the portable DRIFTS measurements. Portable X-Ray fluorescence and surface gloss readings were also made at the pFTIR spot locations to complement the results. Using known dry varnish samples, pFTIR reference spectra were obtained and a DRIFT spectral library was also created from known historic batches of varnishes used by the museum. These were then compared with the in situ pFTIR surface readings taken from the paintings together with additional spectra acquired from a selected number of micro-samples from the same spot locations. The preliminary measurements provided an insight into the capabilities, limitations and practical aspects of using portable DRIFTS for the identification of varnish coatings present in this specific selection of Munch paintings.

Radiocarbon dating

“…Thorough spectral analysis and characterization methods of sample material is essential in choosing most promising fraction or component. For example, proper selection of the binder or pigments from paintings for radiocarbon dating requires characterization of the paint layer using FTIR 274,275 , Raman spectroscopy, X-ray fluorescence 276 , X-ray diffraction and/or gas chromatography-mass spectrometry [277][278][279][280] . These tools are also useful to control the purity of fibers, wood and paper.…”

“…The F 14 C in fat cells, blood, nails, hair, skin collagen and bone lipids, which are constantly renewing, is in equilibrium with the diet's 14 C signature 256 372 . (lead white), canvas or wood are inspected under a stereomicroscope, and analysed using arrange of techniques including FTIR 274,275 , Raman spectroscopy 373,374 , XRF 276 , XRD 375 , GC-MS [277][278][279][280] to assist in the formulation of appropriate research questions and sampling strategies.…”

Removal of a Past Varnish Treatment from a 19th-Century Belgian Wall Painting by Means of a Solvent-Loaded Double Network Hydrogel

“…The collected varnish films were analyzed by ATR–FTIR spectroscopy [ 44 , 45 ]. All the analyzed films showed the same spectra, indicating that only one varnish type was used in the past conservation treatment.…”

Spectroscopic Methods Used in Implant Material Studies

“…Other frequently mentioned advantages include: effortless sample preparation, very good signal-to-noise ratio, and ability to perform in situ measurements and quantitative analysis of surface species [96]. DRIFTS is most often applied to provide precious insights about mechanisms and reaction pathways [97][98][99], organic paints, and dyes [100,101]. It has also proven useful in implant-related studies.…”